First fight: He was reduced to a spectator and called off the dogs because he wanted a rematch down the line.
Second fight: He was changing the subject and shyt.
"
Vegeta, did you feel that power?
It's awful. Must be Majin Buu. We're responsible for this. Guess we have to cancel our fight and stop him.
"
Vegeta put that nikka to sleep and he wakes up, rids himself of all responsibility and plays around with Fat Buu
So pretty much he was just trying to duck the fade with Vegeta. It's hard to come back after losing twice. Look how Cormier was after Jones 2. Goku has to be the most deceitful ass anime character.